As a conventional coordinate input device, a device which senses an image of a beam spot on a screen using a CCD area sensor or linear sensor, and computes and outputs a coordinate value by an image process using a barycentric coordinate position or pattern matching, or the like, a device which uses a position detection element called a PSD (an analog device which can obtain an output voltage corresponding to the spot position), and the like are known.
For example, Japanese Patent Publication No. 7-76902 discloses a device which detects a coordinate position by sensing an image of a beam spot formed by a collimated beam of visible light, and transmitting/receiving control signals by infrared divergent light. Also, Japanese Patent Laid-Open No. 6-274266 discloses a device which detects a coordinate position using a linear CCD sensor and special optical mask.
On the other hand, U.S. Pat. No. 2,503,182 discloses the arrangement of a device using a PSD and a correction method of the output coordinate position.
In recent years, a large-screen display tends to have a larger screen size and higher resolution simultaneously with improvement of brightness. For this reason, the resolving power of a coordinate input device must be improved.
Conventionally, as a coordinate input device of this type, a compact, inexpensive device which uses a ring CCD and is resistant against disturbance light, has been proposed. This coordinate input device has a resolving power 2N times the actual number of pixels by segmenting CCD pixels by computations. For example, to cope with a larger screen, when a CCD having 64 pixels is used and the screen is segmented into 1,024 blocks, a coordinate input device for a large screen can be constructed in principle by simply segmenting one pixel into 16 blocks. However, in such case, although high resolving power can be achieved, the device is vulnerable to the influence of disturbance light or the like other than the input light from the pointing tool.